# System request

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Computer key

"SysReq" redirects here. For prerequisites for computer software, see [System requirements](/source/System_requirements).

A 104-key [PC](/source/Personal_computer) [US](/source/United_States) [English](/source/English_language) [keyboard layout](/source/Keyboard_layout) with System Request circled

**System Request** (**SysRq** or **Sys Req**) is a key on [personal computer](/source/IBM_PC_compatible) [keyboards](/source/Computer_keyboard) that has no standard use. Introduced by [IBM](/source/IBM) with the [PC/AT](/source/IBM_Personal_Computer%2FAT), it was intended to be available as a special key to directly invoke low-level [operating system](/source/Operating_system) functions with no possibility of conflicting with any existing software. A special [BIOS](/source/BIOS) routine—software interrupt 0x15, subfunction 0x85[1]—was added to signal the [OS](/source/Operating_system) when SysRq was pushed or released. Unlike most keys, when it is pressed nothing is stored in the [keyboard buffer](/source/Keyboard_buffer).

## History

The specific low-level function intended for the SysRq key was to switch between operating systems. When the original IBM-PC was created in 1980, there were three leading competing operating systems: [PC DOS](/source/PC_DOS), [CP/M-86](/source/CP%2FM-86), and [UCSD p-System](/source/UCSD_p-System),[2] while [Xenix](/source/Xenix) was added in 1983–1984. The SysRq key was added so that multiple operating systems could be run on the same computer, using the capabilities of the [286](/source/Intel_80286) chip in the PC/AT.[3][*[unreliable source?](https://en.wikipedia.org/wiki/Wikipedia:Reliable_sources)*]

A special key was needed because most [software](/source/Software) of the day operated at a low level, often bypassing the OS entirely, and typically made use of many [hotkey](/source/Hotkey) combinations. The use of [terminate-and-stay-resident](/source/Terminate-and-stay-resident) (TSR) programs further complicated matters. To implement a [task switching](/source/Context_switch) or [multitasking](/source/Computer_multitasking) environment, it was thought that a special, separate key was needed. This is similar to the way "[Control-Alt-Delete](/source/Control-Alt-Delete)" is used under [Windows NT](/source/Windows_NT).

On 84-key keyboards (except the 84-key IBM Model M space saver keyboard), SysRq was a key of its own. On the later 101-key keyboard, it shares a physical key with the [Print screen](/source/Print_screen) key function. The [Alt key](/source/Alt_key) must be held down while pressing this dual-function key to invoke SysRq. This continues through modern PC keyboards.[4]

The default BIOS keyboard routines simply ignore SysRq and return without taking action. So did the [MS-DOS](/source/MS-DOS) input routines. The keyboard routines in [libraries](/source/Library_(software)) supplied with many high-level languages followed suit. Although it is still included on most PC keyboards manufactured, and though it is used by some[*[which?](https://en.wikipedia.org/wiki/Wikipedia:Avoid_weasel_words)*] debugging software, the key is of no use for the vast majority of users.

On the [Hyundai/Hynix](/source/Hynix) Super-16 computer, pressing Ctrl+SysRq will hard boot the system (it will reboot when Ctrl+Alt+Del is unresponsive, and it will invoke startup memory tests that are bypassed on soft-boot).[*[citation needed](https://en.wikipedia.org/wiki/Wikipedia:Citation_needed)*]

## Modern uses

In [Linux](/source/Linux), the [kernel](/source/Kernel_(operating_system)) can be configured to provide functions for system [debugging](/source/Debugging) and crash recovery.[5] This use is known as the "[magic SysRq key](/source/Magic_SysRq_key)".

[Microsoft](/source/Microsoft) has also used SysRq for various [OS](/source/Operating_system)- and [application](/source/Application_software)-level [debuggers](/source/Debugger). In the [CodeView debugger](/source/CodeView), it was sometimes used to break into the debugging during program execution.[6] For the [Windows NT](/source/Windows_NT) remote kernel debugger, it can be used to force the system into the debugger.[7]

On modern Windows and some Linux desktop environments "[Alt](/source/Alt_key) + [Print screen](/source/Print_screen)" (which is the shortcut for SysRq on most modern keyboards[4]) copies an image of the current active window, instead of the entire screen as Print Screen alone would.[8]

## Similar keys

[IBM 3270](/source/IBM_3270)-type console keyboards of the IBM [System/370](/source/System%2F370) [mainframe computer](/source/Mainframe_computer), created in 1970, had an operator interrupt key that was used to cause the operating system such as [VM/370](/source/VM%2F370) or [MVS](/source/MVS) to allow the console to give input to the operating system.

## See also

- [Serial console](/source/Serial_console)

- [Break key](/source/Break_key)

- [Scroll Lock](/source/Scroll_Lock)

## References

1. **[^](#cite_ref-intlist_1-0)** ["Ralf Brown's Interrupt List"](https://www.delorie.com/djgpp/doc/rbinter/id/30/15.html). Retrieved 2018-06-21.

1. **[^](#cite_ref-2)** ["Original IBM PC Product fact sheet"](https://web.archive.org/web/20060814072427/http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html). IBM Information Systems Division. August 12, 1981. Archived from [the original](http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_fact.html) on August 14, 2006. Retrieved January 13, 2010.

1. **[^](#cite_ref-3)** Personal interview with Sandy Meade, creator of the SysRq key

1. ^ [***a***](#cite_ref-modern_4-0) [***b***](#cite_ref-modern_4-1) ["What Are the Sys Rq, Scroll Lock, and Pause Break Keys on My Keyboard?"](https://www.howtogeek.com/125315/htg-explains-what-are-the-sys-rq-scroll-lock-and-pausebreak-keys-on-my-keyboard/). 26 September 2016. Retrieved March 2, 2020.

1. **[^](#cite_ref-linux_5-0)** ["Linux Magic System Request Key Hacks"](https://www.kernel.org/doc/html/latest/admin-guide/sysrq.html). *Linux kernel*. Retrieved 2018-06-21.

1. **[^](#cite_ref-mskb43648_6-0)** ["Returning Control to CodeView"](https://web.archive.org/web/20081108021540/http://support.microsoft.com/kb/43648). *Microsoft Knowledge Base*. Archived from [the original](http://support.microsoft.com/kb/43648) on November 8, 2008. Retrieved January 8, 2008.

1. **[^](#cite_ref-mskb900093_7-0)** ["How to enable a remote kernel debugger connection on a computer that is running Windows Server 2003 with Service Pack 1"](https://web.archive.org/web/20121021034022/http://support.microsoft.com/kb/900093). *Microsoft Knowledge Base*. Archived from [the original](http://support.microsoft.com/kb/900093) on October 21, 2012. Retrieved January 8, 2008.

1. **[^](#cite_ref-8)** ["Copy the window or screen contents"](https://support.microsoft.com/en-us/office/copy-the-window-or-screen-contents-98c41969-51e5-45e1-be36-fb9381b32bb7). Retrieved March 2, 2020.

## External links

- Media related to [System request](https://commons.wikimedia.org/wiki/Category:System_request) at Wikimedia Commons

IBM PC keyboard (Windows, ANSI US layout) v t e Esc F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 PrtSc/ SysRq Scroll Lock Pause/ Break Insert Home Page Up Num Lock ∕ ∗ − Delete End Page Down 7 8 9 + 4 5 6 ↑ 1 2 3 Enter ← ↓ → 0 Ins . Del

v t e Keyboard keys Dead keys Compose Gold Modifier keys Control Shift Alt / Option (Apple) AltGr Command (Apple) / Windows (Microsoft) / Super Meta Hyper Fn Lock keys Scroll Lock Num Lock Caps Lock F-Lock Navigation keys Arrow keys Page Up/Page Down Home End Esc Menu Editing Enter/Return Carriage return Backspace Insert Delete Tab Space bar Numeric keypad Language input Contextual Function keys Print Screen System request Break/Pause Misc. Power management keys (Power, Sleep, Wake) Any key Macro key Menu key Keyboard technology Keyboard shortcut Keyboard layout Keyboard mapping

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Adapted from the Wikipedia article [System request](https://en.wikipedia.org/wiki/System_request) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/System_request?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.